1. Field of the Invention
The invention relates generally to an apparatus and method for collecting and mixing two biological/pharmaceutical liquids. The invention may be used in connection with a method and apparatus for collecting whole blood from a donor and mixing the blood with anticoagulant fluids.
2. Description of the Related Art
During surgical procedures, blood is suctioned from surgical cavities using a suction wand that is connected to a blood reservoir for collecting the aspirated blood for later return to the patient. When handling blood in an extracorporeal device, blood readily tends to clot, making it unacceptable for reinfusion into a patient. Thus, it is often desirable to add an anticoagulant to the blood as it is aspirated. Typically, anticoagulant is added proximate the point of initial collection, such as through a side port of the suction wand or into a blood flow passageway adjacent to the suction wand.
In the conventional system, the suction wand is permanently in fluid communication with the blood reservoir where typically, in the case of a hard shell reservoir, a partial vacuum is created. When the suction wand is used, the infusion of anticoagulant is manually controlled by an operator.
If large influxes of blood are encountered during a procedure, it is up to the operator to recognize that additional anticoagulant is needed, and appropriately adjust the anticoagulant flow rate. In general, the operator will try to maintain a fixed ratio of anticoagulant to blood. The target ratio is usually predetermined based upon the anticoagulant being used and any other relevant data (e.g., the type of surgical procedure).
A drawback of this system is its inaccuracy. Because the flow rate and volumes of anticoagulant are manually controlled by the operator using a roller clamp on flexible tubing, the procedure has a high degree of variability. Not only are the initial settings inexact, they have a tendency to change with time caused by changes in the tubing, fluid height changes, and pressure changes in the system.
Another drawback of the related art system is that it does not fit the erratic occurrence and variable flow rate of blood losses, whereas each time the suction wand is used, varying amounts of anticoagulant are usually needed. For example, more anticoagulant is needed as the suction wand draws only blood than when the wand draws a combination of blood and air. However, with the conventional system, unless an operator intervenes, the same amount of anticoagulant is infused into the blood passageway regardless of the amount of blood being suctioned. Even if an operator intervenes, it is difficult to manually achieve a target ratio. Thus, with the conventional apparatus and method, it is possible to infuse too much or too little anticoagulant into the blood, which could lead to dangerous medical conditions.